A color picture tube includes an electron gun for generating and directing three electron beams to the screen of the tube. The screen is located on the inner surface of a faceplate of the tube and is made up of an array of elements of three different color-emitting phosphors. A color selection electrode, which may be either a shadow mask or a focus mask, is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam.
One type of color picture tube has a tension mask mounted within a faceplate panel thereof. In order to maintain the tension on the mask, the mask must be attached to a support frame. In making a tension mask-frame assembly, the mask is attached to the frame while the frame is held in a compressed condition. After attachment of the mask to the frame, such as by welding, the frame compression is released, so that the frame springs outwardly to tension the mask. The conventional method for compressing the frame is to press on the frame members with blades shaped to provide the proper frame deflection for the desired mask tension distribution. Slight distortions of the frame, especially in frames made of relatively thin material, can result in undesirable uneven tensioning of the mask. Such undesirable variations in tension arise because of the conventional method reliance on fixed displacement inputs to the frame to provide a tension distribution.